Biodegradable aliphatic polyester for use in nonwoven webs

ABSTRACT

A method for forming a biodegradable aliphatic polyester suitable for use in fibers is provided. In one embodiment, for example, an aliphatic polyester is melt blended with an alcohol to initiate an alcoholysis reaction that results in a polyester having one or more hydroxyalkyl or alkyl terminal groups. By selectively controlling the alcoholysis conditions (e.g., alcohol and polymer concentrations, catalysts, temperature, etc.), a modified aliphatic polyester may be achieved that has a molecular weight lower than the starting aliphatic polyester Such lower molecular weight polymers also have the combination of a higher melt flow index and lower apparent viscosity, which is useful in a wide variety of fiber forming applications, such as in the meltblowing of nonwoven webs.

BACKGROUND OF THE INVENTION

Biodegradable nonwoven webs are useful in a wide range of applications,such as in the formation of disposable absorbent products (e.g.,diapers, training pants, sanitary wipes, feminine pads and liners, adultincontinence pads, guards, garments, etc.). To facilitate formation ofthe nonwoven web, a biodegradable polymer should be selected that ismelt processable, yet also has good mechanical and physical properties.Biodegradable aliphatic polyesters (e.g., polybutylene succinate) havebeen developed that possess good mechanical and physical properties.Although various attempts have been made to use aliphatic polyesters inthe formation of nonwoven webs, their relatively high molecular weightand viscosity have generally restricted their use to only certain typesof fiber forming processes. For example, conventional aliphaticpolyesters are not typically suitable for meltblowing processes, whichrequire a low polymer viscosity for successful microfiber formation. Assuch, a need currently exists for a biodegradable aliphatic polyesterthat exhibits good mechanical and physical properties, but which may bereadily formed into a nonwoven web using a variety of techniques (e.g.,meltblowing).

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a method forforming a biodegredable polymer for use in fiber formation is disclosed.The method comprises melt blending a first aliphatic polyester with atleast one alcohol so that the polyester undergoes an alcoholysisreaction. The alcoholysis reaction results in a second, modifiedaliphatic polyester having a melt flow index that is greater than themelt flow index of the first polyester, determined at a load of 2160grams and temperature of 170° C. in accordance with ASTM Test MethodD1238-E.

In accordance with another embodiment of the present invention, a fiberis disclosed that comprises a biodegradable aliphatic polyesterterminated with an alkyl group, hydroxyalkyl group, or a combinationthereof. The polyester has a melt flow index of from about 5 to about1000 grams per 10 minutes, determined at a load of 2160 grams andtemperature of 170° C. in accordance with ASTM Test Method D1238-E.

Other features and aspects of the present invention are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a schematic illustration of a process that may be used in oneembodiment of the present invention to form a nonwoven web;

FIG. 2 is a graph depicting apparent viscosity versus various shearrates for the extruded resins of Example 1;

FIG. 3 is a graph depicting apparent viscosity versus various shearrates for the extruded resins of Example 2;

FIG. 4 shows an SEM microphotograph (500×) of a meltblown web formed inExample 3 (17 gsm sample, Table 6); and

FIG. 5 shows an SEM microphotograph (1000×) of a meltblown web formed inExample 3 (17 gsm sample, Table 6).

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

Reference now will be made in detail to various embodiments of theinvention, one or more examples of which are set forth below. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations may be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, may be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Definitions

As used herein, the term “biodegradable” or “biodegradable polymer”generally refers to a material that degrades from the action ofnaturally occurring microorganisms, such as bacteria, fungi, and algae;environmental heat; moisture; or other environmental factors. Thebiodegradability of a material may be determined using ASTM Test Method5338.92.

As used herein, the term “fibers” refer to elongated extrudates formedby passing a polymer through a forming orifice such as a die. Unlessnoted otherwise, the term “fibers” includes discontinuous fibers havinga definite length and substantially continuous filaments. Substantiallyfilaments may, for instance, have a length much greater than theirdiameter, such as a length to diameter ratio (“aspect ratio”) greaterthan about 15,000 to 1, and in some cases, greater than about 50,000 to1.

As used herein, the term “monocomponent” refers to fibers formed onepolymer. Of course, this does not exclude fibers to which additives havebeen added for color, anti-static properties, lubrication,hydrophilicity, liquid repellency, etc.

As used herein, the term “multicomponent” refers to fibers formed fromat least two polymers (e.g., bicomponent fibers) that are extruded fromseparate extruders. The polymers are arranged in substantiallyconstantly positioned distinct zones across the cross-section of thefibers. The components may be arranged in any desired configuration,such as sheath-core, side-by-side, pie, island-in-the-sea, and so forth.Various methods for forming multicomponent fibers are described in U.S.Pat. No. 4,789,592 to Tanicuchi et al. and U.S. Pat. Nos. 5,336,552 toStrack et al., 5,108,820 to Kaneko, et al., 4,795,668 to Kruege, et al.,5,382,400 to Pike, et al., 5,336,552 to Strack, et al., and 6,200,669 toMarmon, et al., which are incorporated herein in their entirety byreference thereto for all purposes. Multicomponent fibers having variousirregular shapes may also be formed, such as described in U.S. Pat. No.5,277,976 to Hogle, et al., U.S. Pat. No. 5,162,074 to Hills, U.S. Pat.No. 5,466,410 to Hills, U.S. Pat. No. 5,069,970 to Largman, et al., andU.S. Pat. No. 5,057,368 to Largman, et al., which are incorporatedherein in their entirety by reference thereto for all purposes.

As used herein, the term “multiconstituent” refers to fibers formed fromat least two polymers (e.g., biconstituent fibers) that are extrudedfrom the same extruder. The polymers are not arranged in substantiallyconstantly positioned distinct zones across the cross-section of thefibers. Various multiconstituent fibers are described in U.S. Pat. No.5,108,827 to Gessner, which is incorporated herein in its entirety byreference thereto for all purposes.

As used herein, the term “nonwoven web” refers to a web having astructure of individual fibers that are randomly interlaid, not in anidentifiable manner as in a knitted fabric. Nonwoven webs include, forexample, meltblown webs, spunbond webs, carded webs, wet-laid webs,airlaid webs, coform webs, hydraulically entangled webs, etc. The basisweight of the nonwoven web may generally vary, but is typically fromabout 5 grams per square meter (“gsm”) to 200 gsm, in some embodimentsfrom about 10 gsm to about 150 gsm, and in some embodiments, from about15 gsm to about 100 gsm.

As used herein, the term “meltblown” web or layer generally refers to anonwoven web that is formed by a process in which a molten thermoplasticmaterial is extruded through a plurality of fine, usually circular, diecapillaries as molten fibers into converging high velocity gas (e.g.air) streams that attenuate the fibers of molten thermoplastic materialto reduce their diameter, which may be to microfiber diameter.Thereafter, the meltblown fibers are carried by the high velocity gasstream and are deposited on a collecting surface to form a web ofrandomly dispersed meltblown fibers. Such a process is disclosed, forexample, in U.S. Pat. No. 3,849,241 to Butin, et al.; U.S. Pat. No.4,307,143 to Meitner, et al.; and U.S. Pat. No. 4,707,398 to Wisneski,et al., which are incorporated herein in their entirety by referencethereto for all purposes. Meltblown fibers may be substantiallycontinuous or discontinuous, and are generally tacky when deposited ontoa collecting surface.

As used herein, the term “spunbond” web or layer generally refers to anonwoven web containing small diameter substantially continuousfilaments. The filaments are formed by extruding a molten thermoplasticmaterial from a plurality of fine, usually circular, capillaries of aspinnerette with the diameter of the extruded filaments then beingrapidly reduced as by, for example, eductive drawing and/or otherwell-known spunbonding mechanisms. The production of spunbond webs isdescribed and illustrated, for example, in U.S. Pat. No. U.S. Pat. No.4,340,563 to Appel, et al., U.S. Pat. No. 3,692,618 to Dorschner, etal., U.S. Pat. No. 3,802,817 to Matsuki, et al., U.S. Pat. No. 3,338,992to Kinney, U.S. Pat. No. 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 toHartman, U.S. Pat. No. 3,502,538 to Levy, U.S. Pat. No. 3,542,615 toDobo, et al., and U.S. Pat. No. 5,382,400 to Pike, et al., which areincorporated herein in their entirety by reference thereto for allpurposes. Spunbond filaments are generally not tacky when they aredeposited onto a collecting surface. Spunbond filaments may sometimeshave diameters less than about 40 micrometers, and are often betweenabout 5 to about 20 micrometers.

As used herein, the term “carded web” refers to a web made from staplefibers that are sent through a combing or carding unit, which separatesor breaks apart and aligns the staple fibers in the machine direction toform a generally machine direction-oriented fibrous nonwoven web. Suchfibers are usually obtained in bales and placed in an opener/blender orpicker, which separates the fibers prior to the carding unit. Onceformed, the web may then be bonded by one or more known methods.

As used herein, the term “airlaid web” refers to a web made from bundlesof fibers having typical lengths ranging from about 3 to about 19millimeters (mm). The fibers are separated, entrained in an air supply,and then deposited onto a forming surface, usually with the assistanceof a vacuum supply. Once formed, the web is then bonded by one or moreknown methods.

As used herein, the term “coform web” generally refers to a compositematerial containing a mixture or stabilized matrix of thermoplasticfibers and a second non-thermoplastic material. As an example, coformmaterials may be made by a process in which at least one meltblown diehead is arranged near a chute through which other materials are added tothe web while it is forming. Such other materials may include, but arenot limited to, fibrous organic materials such as woody or non-woodypulp such as cotton, rayon, recycled paper, pulp fluff and alsosuperabsorbent particles, inorganic and/or organic absorbent materials,treated polymeric staple fibers and so forth. Some examples of suchcoform materials are disclosed in U.S. Pat. No. 4,100,324 to Anderson,et al.; U.S. Pat. No. 5,284,703 to Everhart, et al.; and U.S. Pat. No.5,350,624 to Georger, et al.; which are incorporated herein in theirentirety by reference thereto for all purposes.

Detailed Description

The present invention is directed to a method for forming abiodegradable aliphatic polyester suitable for use in fibers. In oneembodiment, for example, an aliphatic polyester is melt blended with analcohol to initiate an alcoholysis reaction that results in a polyesterhaving one or more hydroxyalkyl or alkyl terminal groups. By selectivelycontrolling the alcoholysis conditions (e.g., alcohol and polymerconcentrations, catalysts, temperature, etc.), a modified aliphaticpolyester may be achieved that has a molecular weight lower than thestarting aliphatic polymer. Such lower molecular weight polymers alsohave the combination of a higher melt flow index and lower apparentviscosity, which is useful in a wide variety of fiber formingapplications, such as in the meltblowing of nonwoven webs.

I. Reaction Components

A. Aliphatic Polyester

Aliphatic polyesters are generally synthesized from the polymerizationof a polyol with an aliphatic carboxylic acid or anhydride thereof.Generally speaking, the carboxylic acid monomer constituents of thepolyester are predominantly aliphatic in nature in that they lackaromatic rings. For example, at least about 80 mol. %, in someembodiments at least about 90 mol. %, and in some embodiments, at leastabout 95 mol. % of the carboxylic acid monomer constituents may bealiphatic monomers. In one particular embodiment, the carboxylic acidmonomer constituents are formed from aliphatic dicarboxylic acids (oranhydrides thereof). Representative aliphatic dicarboxylic acids thatmay be used to form the aliphatic polyester may include substituted orunsubstituted, linear or branched, non-aromatic dicarboxylic acidsselected from aliphatic dicarboxylic acids containing 2 to about 12carbon atoms, and derivatives thereof. Non-limiting examples ofaliphatic dicarboxylic acids include malonic, succinic, oxalic,glutaric, adipic, pimelic, azelaic, sebacic, fumaric, 2,2-dimethylglutaric, suberic, 1,3-cyclopentanedicarboxylic,1,4-cyclohexanedicarboxylic, 1,3-cyclohexanedicarboxylic, diglycolic,itaconic, maleic, and 2,5-norbornanedicarboxylic.

Suitable polyols used to form the aliphatic polyester may be substitutedor unsubstituted, linear or branched, polyols selected from polyolscontaining 2 to about 12 carbon atoms and polyalkylene ether glycolscontaining 2 to 8 carbon atoms. Examples of polyols that may be usedinclude, but are not limited to, ethylene glycol, diethylene glycol,propylene glycol, 1,2-propanediol, 1,3-propanediol,2,2-dimethyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,6-hexanediol,polyethylene glycol, diethylene glycol, 2,2,4-trimethyl-1,6-hexanediol,thiodiethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, cyclopentanediol, triethyleneglycol, and tetraethylene glycol. Preferred polyols include1,4-butanediol; 1,3-propanediol; ethylene glycol; 1,6-hexanediol;diethylene glycol; and 1,4-cyclohexanedimethanol.

The polymerization may be catalyzed by a catalyst, such as atitanium-based catalyst (e.g., tetraisopropyltitanate, tetraisopropoxytitanium, dibutoxydiacetoacetoxy titanium, or tetrabutyltitanate). Ifdesired, a diisocyanate chain extender may be reacted with the polyesterto increase its molecular weight. Representative diisocyanates mayinclude toluene 2,4-diisocyanate, toluene 2,6-diisocyanate,2,4′-diphenylmethane diisocyanate, naphthylene-1,5-diisocyanate,xylylene diisocyanate, hexamethylene diisocyanate (“HMDI”), isophoronediisocyanate and methylenebis(2-isocyanatocyclohexane). Trifunctionalisocyanate compounds may also be employed that contain isocyanurateand/or biurea groups with a functionality of not less than three, or toreplace the diisocyanate compounds partially by tri- or polyisocyanates.The preferred diisocyanate is hexamethylene diisocyanate. The amount ofthe chain extender employed is typically from about 0.3 to about 3.5 wt.%, in some embodiments, from about 0.5 to about 2.5 wt. % based on thetotal weight percent of the polymer.

The polyester may either be a linear polymer or a long-chain branchedpolymer. Long-chain branched polymers are generally prepared by using alow molecular weight branching agent, such as a polyol, polycarboxylicacid, hydroxy acid, and so forth. Representative low molecular weightpolyols that may be employed as branching agents include glycerol,trimethylolpropane, trimethylolethane, polyethertriols, glycerol,1,2,4-butanetriol, pentaerythritol, 1,2,6-hexanetriol, sorbitol,1,1,4,4-tetrakis(hydroxymethyl)cyclohexane, tris(2-hydroxyethyl)isocyanurate, and dipentaerythritol. Representative higher molecularweight polyols (molecular weight of 400 to 3000) that may be used asbranching agents include triols derived by condensing alkylene oxideshaving 2 to 3 carbons, such as ethylene oxide and propylene oxide withpolyol initiators. Representative polycarboxylic acids that may be usedas branching agents include hemimellitic acid, trimellitic(1,2,4-benzenetricarboxylic) acid and anhydride,trimesic(1,3,5-benzenetricarboxylic) acid, pyromellitic acid andanhydride, benzenetetracarboxylic acid, benzophenone tetracarboxylicacid, 1,1,2,2-ethanetetracarboxylic acid, 1,1,2-ethanetricarboxylicacid, 1,3,5-pentanetricarboxylic acid, and1,2,3,4-cyclopentanetetracarboxylic acid. Representative hydroxy acidsthat may be used as branching agents include malic acid, citric acid,tartaric acid, 3-hydroxyglutaric acid, mucic acid, trihydroxyglutaricacid, 4-carboxyphthalic anhydride, hydroxyisophthalic acid, and4-(beta-hydroxyethyl)phthalic acid. Such hydroxy acids contain acombination of 3 or more hydroxyl and carboxyl groups. Especiallypreferred branching agents include trimellitic acid, trimesic acid,pentaerythritol, trimethylol propane and 1,2,4-butanetriol.

In one particular embodiment, the aliphatic polyester has the followinggeneral structure:

wherein,

m is an integer from 2 to 10, in some embodiments from 3 to 8, and insome embodiments from 2 to 4;

n is an integer from 0 to 18, in some embodiments from 1 to 12, and insome embodiments, from 2 to 4; and

x is an integer greater than 1. Specific examples of such aliphaticpolyesters include succinate-based aliphatic polymers, such aspolybutylene succinate, polyethylene succinate, polypropylene succinate,and copolymers thereof (e.g., polybutylene succinate adipate);oxalate-based aliphatic polymers, such as polyethylene oxalate,polybutylene oxalate, polypropylene oxalate, and copolymers thereof;malonate-based aliphatic polymers, such as polyethylene malonate,polypropylene malonate, polybutylene malonate, and copolymers thereof;adipate-based aliphatic polymers, such as polyethylene adipate,polypropylene adipate, polybutylene adipate, and polyhexylene adipate,and copolymers thereof; etc., as well as blends of any of the foregoing.Polybutylene succinate, which has the following structure, isparticularly desirable:

One specific example of a suitable polybutylene succinate polymer iscommercially available from IRE Chemicals (South Korea) under thedesignation ENPOL™ G4500. Other suitable polybutylene succinate resinsmay include those available under the designation BIONOLLE® from ShowaHighpolymer Company (Tokyo, Japan). Still other suitable aliphaticpolyesters may be described in U.S. Pat. Nos. 5,714,569; 5,883,199;6,521,336; and 6,890,989, which are incorporated herein in theirentirety by reference thereto for all purposes.

The aliphatic polyester typically has a number average molecular weight(“M_(n)”) ranging from about 60,000 to about 160,000 grams per mole, insome embodiments from about 80,000 to about 140,000 grams per mole, andin some embodiments, from about 100,000 to about 120,000 grams per mole.Likewise, the polymer also typically has a weight average molecularweight (“M_(w)”) ranging from about 80,000 to about 200,000 grams permole, in some embodiments from about 100,000 to about 180,000 grams permole, and in some embodiments, from about 110,000 to about 160,000 gramsper mole. The ratio of the weight average molecular weight to the numberaverage molecular weight (“M_(w)/M_(n)”), i.e., the “polydispersityindex”, is also relatively low. For example, the polydispersity indextypically ranges from about 1.0 to about 3.0, in some embodiments fromabout 1.1 to about 2.0, and in some embodiments, from about 1.2 to about1.8. The weight and number average molecular weights may be determinedby methods known to those skilled in the art.

The aliphatic polyester may also have an apparent viscosity of fromabout 100 to about 1000 Pascal seconds (Pa·s), in some embodiments fromabout 200 to about 800 Pa·s, and in some embodiments, from about 300 toabout 600 Pass, as determined at a temperature of 150° C. and a shearrate of 1000 sec⁻¹. The melt flow index of the aliphatic polyester mayalso range from about 0.1 to about 10 grams per 10 minutes, in someembodiments from about 0.5 to about 8 grams per 10 minutes, and in someembodiments, from about 1 to about 5 grams per 10 minutes. The melt flowindex is the weight of a polymer (in grams) that may be forced throughan extrusion rheometer orifice (0.0825-inch diameter) when subjected toa load of 2160 grams in 10 minutes at a certain temperature (e.g., 170°C.), measured in accordance with ASTM Test Method D1238-E.

The aliphatic polymer also typically has a melting point of from about50° C. to about 160° C., in some embodiments from about 80° C. to about160° C., and in some embodiments, from about 100° C. to about 140° C.Such low melting point polyesters are useful in that they biodegrade ata fast rate and are generally soft. The glass transition temperature(“T_(g)”) of the polyester is also relatively low to improve flexibilityand processability of the polymers. For example, the T_(g) may be about25° C. or less, in some embodiments about 0° C. or less, and in someembodiments, about −10° C. or less. As discussed in more detail below,the melting temperature and glass transition temperature may all bedetermined using differential scanning calorimetry (“DSC”) in accordancewith ASTM D-3417.

B. Alcohol

As indicated above, the aliphatic polyester may be reacted with analcohol to form a modified aliphatic polyester having a reducedmolecular weight. The concentration of the alcohol reactant mayinfluence the extent to which the molecular weight is altered. Forinstance, higher alcohol concentrations generally result in a moresignificant decrease in molecular weight. Of course, too high of analcohol concentration may also affect the physical characteristics ofthe resulting polymer. Thus, in most embodiments, the alcohol(s) areemployed in an amount of about 0.1 wt. % to about 20 wt. %, in someembodiments from about 0.2 wt. % to about 10 wt. %, and in someembodiments, from about 0.5 wt. % to about 5 wt. %, based on the totalweight of the starting aliphatic polyester.

The alcohol may be monohydric or polyhydric (dihydric, trihydric,tetrahydric, etc.), saturated or unsaturated, and optionally substitutedwith functional groups, such as carboxyl, amine, etc. Examples ofsuitable monohydric alcohols include methanol, ethanol, 1-propanol,2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol,1-hexanol, 2-hexanol, 3-hexanol, 1-heptanol, 2-heptanol, 3-heptanol,4-heptanol, 1-octanol, 2-octanol, 3-octanol, 4-octanol, 1-nonanol,2-nonanol, 3-nonanol, 4-nonanol, 5-nonanol, 1-decanol, 2-decanol,3-decanol, 4-decanol, 5-decanol, allyl alcohol, 1-butenol, 2-butenol,1-pentenol, 2 pentenol, 1-hexenol, 2-hexenol, 3-hexenol, 1-heptenol,2-heptenol, 3-heptenol, 1-octenol, 2-octenol, 3-octenol, 4-octenol,1-nonenol, 2-nonenol, 3-nonenol, 4-nonenol, 1-decenol, 2-decenol,3-decenol, 4-decenol, 5-decenol, cyclohexanol, cyclopentanol,cycloheptanol, 1-phenylhyl alcohol, 2-phenylhyl alcohol,2-ethoxyethanol, methanolamine, ethanolamine, and so forth. Examples ofsuitable dihydric alcohols include 1,3-propanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,1-hydroxymethyl-2-hydroxyethylcyclohexane,1-hydroxy-2-hydroxypropylcyclohexane,1-hydroxy-2-hydroxyethylcyclohexane,1-hydroxymethyl-2-hydroxyethylbenzene,1-hydroxymethyl-2-hydroxypropylbenzene, 1-hydroxy-2-hydroxyethylbenzene,1,2-benzylmethylol, 1,3-benzyldimethylol, and so forth. Suitabletrihydric alcohols may include glycerol, trimethylolpropane, etc., whilesuitable tetrahydric alcohols may include pentaerythritol, erythritol,etc. Preferred alcohols are dihydric alcohols having from 2 to 6 carbonatoms, such as 1,3-propanediol and 1,4-butanediol.

The hydroxy group of the alcohol is generally capable of attacking anester linkage of the starting aliphatic polyester, thereby leading tochain scission or “depolymerization” of the polyester molecule into oneor more shorter ester chains. The shorter chains may include aliphaticpolyesters or oligomers, as well as minor portions of aliphaticpolyesters or oligomers, and combinations of any of the foregoing.Although not necessarily required, the short chain aliphatic polyestersformed during alcoholysis are often terminated with an alkyl and/orhydroxyalkyl groups derived from the alcohol. Alkyl group terminationsare typically derived from monohydric alcohols, while hydroxyalkyl groupterminations are typically derived from polyhydric alcohols. In oneparticular embodiment, for example, an aliphatic polyester is formedduring the alcoholysis reaction having the following general structure:

wherein,

m is an integer from 2 to 10, in some embodiments from 3 to 8, and insome embodiments from 2 to 4;

n is an integer from 0 to 18, in some embodiments from 1 to 12, and insome embodiments, from 2 to 4;

y is an integer greater than 1; and

R₁ and R₂ are independently selected from hydrogen; hydroxyl groups;straight chain or branched, substituted or unsubstituted C₁-C₁₀ alkylgroups; straight chain or branched, substituted or unsubstituted C₁-C₁₀hydroxalkyl groups. Preferably, at least one of R₁ and R₂, or both, arestraight chain or branched, substituted or unsubstituted, C₁-C₁₀ alkylor C₁-C₁₀ hydroxyalkyl groups, in some embodiments C₁-C₈ alkyl or C₁-C₈hydroxyalkyl groups, and in some embodiments, C₂-C₆ alkyl or C₂-C₆hydroxyalkyl groups. Examples of suitable alkyl and hydroxyalkyl groupsinclude, for instance, methyl, ethyl, iso-propyl, n-propyl, n-butyl,isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl,n-decyl, 1-hydroxyethyl, 2-hydroxyethyl, 3-hydroxypropyl,4-hydroxybutyl, and 5-hydroxypentyl groups. Thus, as indicated, themodified aliphatic polyester has a different chemical composition thanan unmodified polyester in terms of its terminal groups. The terminalgroups may play a substantial role in determining the properties of thepolymer, such as its reactivity, stability, etc.

Regardless of its particular structure, a new polymer species is formedduring alcoholysis that has a molecular weight lower than that of thestarting polyester. The weight average and/or number average molecularweights may, for instance, each be reduced so that the ratio of thestarting polyester molecular weight to the new molecular weight is atleast about 1.1, in some embodiments at least about 1.4, and in someembodiments, at least about 1.6. For example, the modified aliphaticpolyester may have a number average molecular weight (“M_(n)”) rangingfrom about 10,000 to about 70,000 grams per mole, in some embodimentsfrom about 20,000 to about 60,000 grams per mole, and in someembodiments, from about 25,000 to about 50,000 grams per mole. Likewise,the modified aliphatic polyester may also have a weight averagemolecular weight (“M_(w)”) of from about 20,000 to about 125,000 gramsper mole, in some embodiments from about 30,000 to about 110,000 gramsper mole, and in some embodiments, from about 40,000 to about 80,000grams per mole.

In addition to possessing a lower molecular weight, the modifiedaliphatic polyester may also have a lower apparent viscosity and highermelt flow index than the starting polyester. The apparent viscosity mayfor instance, be reduced so that the ratio of the starting polyesterviscosity to the modified polyester viscosity is at least about 1.1, insome embodiments at least about 2, and in some embodiments, from about10 to about 40. Likewise, the melt flow index may be increased so thatthe ratio of the modified polyester melt flow index to the startingpolyester melt flow index is at least about 1.5, in some embodiments atleast about 3, in some embodiments at least about 50, and in someembodiments, from about 100 to about 1000. In one particular embodiment,the modified aliphatic polyester may have an apparent viscosity of fromabout 5 to about 500 Pascal seconds (Pa·s), in some embodiments fromabout 10 to about 400 Pass, and in some embodiments, from about 15 toabout 100 Pa·s, as determined at a temperature of 150° C. and a shearrate of 1000 sec⁻¹. The melt flow index of the modified aliphaticpolyester may range from about 5 to about 1000 grams per 10 minutes, insome embodiments from about 10 to about 800 grams per 10 minutes, and insome embodiments, from about 100 to about 700 grams per 10 minutes (170°C., 2.16 kg). Of course, the extent to which the molecular weight,apparent viscosity, and/or melt flow index are altered by thealcoholysis reaction may vary depending on the intended application.

Although differing from the starting polymer in certain properties, themodified aliphatic polyester may nevertheless retain other properties ofthe starting polymer to enhance the flexibility and processability ofthe polymers. For example, the thermal characteristics (e.g., T_(g),T_(m), and latent heat of fusion) typically remain substantially thesame as the starting polymer, such as within the ranges noted above.Further, even though the actual molecular weights may differ, thepolydispersity index of the modified aliphatic polyester may remainsubstantially the same as the starting polymer, such as within the rangeof about 1.0 to about 3.0, in some embodiments from about 1.1 to about2.0, and in some embodiments, from about 1.2 to about 1.8.

C. Catalyst

A catalyst may be employed to facilitate the modification of thealcoholysis reaction. The concentration of the catalyst may influencethe extent to which the molecular weight is altered. For instance,higher catalyst concentrations generally result in a more significantdecrease in molecular weight. Of course, too high of a catalystconcentration may also affect the physical characteristics of theresulting polymer. Thus, in most embodiments, the catalyst(s) areemployed in an amount of about 50 to about 2000 parts per million(“ppm”), in some embodiments from about 100 to about 1000 ppm, and insome embodiments, from about 200 to about 1000 ppm, based on the weightof the starting aliphatic polyester.

Any known catalyst may be used in the present invention to accomplishthe desired reaction. In one embodiment, for example, a transition metalcatalyst may be employed, such as those based on Group IVB metals and/orGroup IVA metals (e.g., alkoxides or salts). Titanium-, zirconium-,and/or tin-based metal catalysts are especially desirable and mayinclude, for instance, titanium butoxide, titanium tetrabutoxide,titanium propoxide, titanium isopropoxide, titanium phenoxide, zirconiumbutoxide, dibutyltin oxide, dibutyltin diacetate, tin phenoxide, tinoctylate, tin stearate, dibutyltin dioctoate, dibutyltin dioleylmaleate,dibutyltin dibutylmaleate, dibutyltin dilaurate,1,1,3,3-tetrabutyl-1,3-dilauryloxycarbonyldistannoxane,dibutyltindiacetate, dibutyltin diacetylacetonate, dibutyltinbis(o-phenylphenoxide), dibutyltin bis(triethoxysilicate), dibutyltindistearate, dibutyltin bis(isononyl-3-mercaptopropionate), dibutyltinbis(isooctyl thioglycolate), dioctyltin oxide, dioctyltin dilaurate,dioctyltin diacetate, and dioctyltin diversatate.

D. Co-Solvent

The alcoholysis reaction is typically carried out in the absence of asolvent other than the alcohol reactant. Nevertheless, a co-solvent maybe employed in some embodiments of the present invention. In oneembodiment, for instance, the co-solvent may facilitate the dispersionof the catalyst in the reactant alcohol. Examples of suitableco-solvents may include ethers, such as diethyl ether, anisole,tetrahydrofuran, ethylene glycol dimethyl ether, triethylene glycoldimethyl ether, tetraethylene glycol dimethyl ether, dioxane, etc.;alcohols, such as methanol, ethanol, n-butanol, benzyl alcohol, ethyleneglycol, diethylene glycol, etc.; phenols, such as phenol, etc.;carboxylic acids, such as formic acid, acetic acid, propionic acid,toluic acid, etc.; esters, such as methyl acetate, butyl acetate, benzylbenzoate, etc.; aromatic hydrocarbons, such as benzene, toluene,ethylbenzene, tetralin, etc.; aliphatic hydrocarbons, such as n-hexane,n-octane, cyclohexane, etc.; halogenated hydrocarbons, such asdichloromethane, trichloroethane, chlorobenzene, etc.; nitro compounds,such as nitromethane, nitrobenzene, etc.; carbamides, such asN,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, etc.;ureas, such as N,N-dimethylimidazolidinone, etc.; sulfones, such asdimethyl sulfone, etc.; sulfoxides, such as dimethyl sulfoxide, etc.;lactones, such as butyrolactone, caprolactone, etc.; carbonic acidesters, such as dimethyl carbonate, ethylene carbonate, etc.; and soforth.

When employed, the co-solvent(s) may be employed in an amount from about0.5 wt. % to about 20 wt. %, in some embodiments from about 0.8 wt. % toabout 10 wt. %, and in some embodiments, from about 1 wt. % to about 5wt. %, based on the weight of the reactive composition. It should beunderstood, however, that a co-solvent is not required. In fact, in someembodiments of the present invention, the reactive composition issubstantially free of any co-solvents, e.g., less than about 0.5 wt. %of the reactive composition.

E. Other Ingredients

Other ingredients may of course be utilized for a variety of differentreasons. For instance, a wetting agent may be employed in someembodiments of the present invention to improve hydrophilicity. Wettingagents suitable for use in the present invention are generallycompatible with aliphatic polyesters. Examples of suitable wettingagents may include surfactants, such as UNITHOX® 480 and UNITHOX® 750ethoxylated alcohols, or UNICID™ acid amide ethoxylates, all availablefrom Petrolite Corporation of Tulsa, Okla. Other suitable wetting agentsare described in U.S. Pat. No. 6,177,193 to Tsai, et al., which isincorporated herein in its entirety by reference thereto for allrelevant purposes. Still other materials that may be used include,without limitation, melt stabilizers, processing stabilizers, heatstabilizers, light stabilizers, antioxidants, pigments, surfactants,waxes, flow promoters, plasticizers, particulates, and other materialsadded to enhance processability. When utilized, such additionalingredients are each typically present in an amount of less than about 5wt. %, in some embodiments less than about 1 wt. %, and in someembodiments, less than about 0.5 wt. %, based on the weight of thestarting aliphatic polyester.

II. Reaction Technique

The alcoholysis reaction may be performed using any of a variety ofknown techniques. In one embodiment, for example, the reaction isconducted while the starting polyester is in the melt phase (“meltblending”) to minimize the need for additional solvents and/or solventremoval processes. The raw materials (e.g., biodegradable polymer,alcohol, catalyst, etc.) may be supplied separately or in combination(e.g., in a solution). The raw materials may likewise be supplied eithersimultaneously or in sequence to a melt-blending device thatdispersively blends the materials. Batch and/or continuous melt blendingtechniques may be employed. For example, a mixer/kneader, Banbury mixer,Farrel continuous mixer, single-screw extruder, twin-screw extruder,roll mill, etc., may be utilized to blend the materials. Oneparticularly suitable melt-blending device is a co-rotating, twin-screwextruder (e.g., ZSK-30 twin-screw extruder available from Werner &Pfleiderer Corporation of Ramsey, N.J.). Such extruders may includefeeding and venting ports and provide high intensity distributive anddispersive mixing, which facilitate the alcoholysis reaction. Forexample, the polyester may be fed to a feeding port of the twin-screwextruder and melted. Thereafter, the alcohol may be injected into thepolymer melt. Alternatively, the alcohol may be separately fed into theextruder at a different point along its length. The catalyst, a mixtureof two or more catalysts, or catalyst solutions may be injectedseparately or in combination with the alcohol or a mixture of two ormore alcohols to the polymer melt.

Regardless of the particular melt blending technique chosen, the rawmaterials are blended under high shear/pressure and heat to ensuresufficient mixing for initiating the alcoholysis reaction. For example,melt blending may occur at a temperature of from about 50° C. to about300° C., in some embodiments, from about 70° C. to about 250° C., and insome embodiments, from about 90° C. to about 180° C. Likewise, theapparent shear rate during melt blending may range from about 100seconds⁻¹ to about 10,000 seconds⁻¹, in some embodiments from about 500seconds⁻¹ to about 5000 seconds⁻¹, and in some embodiments, from about800 seconds⁻¹ to about 1200 seconds⁻¹. The apparent shear rate is equalto 4Q/πR³, where Q is the volumetric flow rate (“m³/s”) of the polymermelt and R is the radius (“m”) of the capillary (e.g., extruder die)through which the melted polymer flows.

III. Fiber Formation

Fibers formed from the modified aliphatic polyester may generally haveany desired configuration, including monocomponent, multicomponent(e.g., sheath-core configuration, side-by-side configuration, pieconfiguration, island-in-the-sea configuration, and so forth), and/ormulticonstituent. In some embodiments, the fibers may contain one ormore strength-enhancing polymers as a component (e.g., bicomponent) orconstituent (e.g., biconstituent) to further enhance strength and othermechanical properties. The strength-enhancing polymer may be athermoplastic polymer that is not generally considered biodegradable,such as polyolefins, e.g., polyethylene, polypropylene, polybutylene,and so forth; polytetrafluoroethylene; polyesters, e.g., polyethyleneterephthalate, and so forth; polyvinyl acetate; polyvinyl chlorideacetate; polyvinyl butyral; acrylic resins, e.g., polyacrylate,polymethylacrylate, polymethylmethacrylate, and so forth; polyamides,e.g., nylon; polyvinyl chloride; polyvinylidene chloride; polystyrene;polyvinyl alcohol; and polyurethanes. More desirably, however, thestrength-enhancing polymer is biodegradable, such as aliphaticpolyesters, aromatic polyesters; aliphatic-aromatic polyesters; andblends thereof.

Any of a variety of processes may be used to form fibers in accordancewith the present invention. Referring to FIG. 1, for example, oneembodiment of a method for forming meltblown fibers is shown. Meltblownfibers form a structure having a small average pore size, which may beused to inhibit the passage of liquids and particles, while allowinggases (e.g., air and water vapor) to pass therethrough. To achieve thedesired pore size, the meltblown fibers are typically “microfibers” inthat they have an average size of 10 micrometers or less, in someembodiments about 7 micrometers or less, and in some embodiments, about5 micrometers or less. The ability to produce such fine fibers may befacilitated in the present invention through the use of a modifiedaliphatic polyester having the desirable combination of low apparentviscosity and high melt flow index.

In FIG. 1, for instance, the raw materials (e.g., polymer, alcohol,catalyst, etc.) are fed into an extruder 12 from a hopper 10. The rawmaterials may be provided to the hopper 10 using any conventionaltechnique and in any state. For example, the alcohol may be supplied asa vapor or liquid. Alternatively, the aliphatic polyester may be fed tothe hopper 10, and the alcohol and optional catalyst (either incombination or separately) may be injected into the polyester melt inthe extruder 12 downstream from the hopper 10. The extruder 12 is drivenby a motor 11 and heated to a temperature sufficient to extrude thepolymer and to initiate the alcoholysis reaction. For example, theextruder 12 may employ one or multiple zones operating at a temperatureof from about 50° C. to about 300° C., in some embodiments, from about70° C. to about 250° C., and in some embodiments, from about 90° C. toabout 180° C. Typical shear rates range from about 100 seconds⁻¹ toabout 10,000 seconds⁻¹, in some embodiments from about 500 seconds⁻¹ toabout 5000 seconds⁻¹, and in some embodiments, from about 800 seconds⁻¹to about 1200 seconds⁻¹.

Once formed, the modified aliphatic polyester may be subsequently fed toanother extruder in a fiber formation line (e.g., extruder 12 of ameltblown spinning line). Alternatively, the modified aliphaticpolyester may be directly formed into a fiber through supply to a die14, which may be heated by a heater 16. It should be understood thatother meltblown die tips may also be employed. As the polymer exits thedie 14 at an orifice 19, high pressure fluid (e.g., heated air) suppliedby conduits 13 attenuates and spreads the polymer stream intomicrofibers 18. Although not shown in FIG. 1, the die 14 may also bearranged adjacent to or near a chute through which other materials(e.g., cellulosic fibers, particles, etc.) traverse to intermix with theextruded polymer and form a “coform” web.

The microfibers 18 are randomly deposited onto a foraminous surface 20(driven by rolls 21 and 23) with the aid of an optional suction box 15to form a meltblown web 22. The distance between the die tip and theforaminous surface 20 is generally small to improve the uniformity ofthe fiber laydown. For example, the distance may be from about 1 toabout 35 centimeters, and in some embodiments, from about 2.5 to about15 centimeters. In FIG. 1, the direction of the arrow 28 shows thedirection in which the web is formed (i.e., “machine direction”) andarrow 30 shows a direction perpendicular to the machine direction (i.e.,“cross-machine direction”). Optionally, the meltblown web 22 may then becompressed by rolls 24 and 26. The desired, denier of the fibers mayvary depending on the desired application. Typically, the fibers areformed to have a denier per filament of less than about 6, in someembodiments less than about 3, and in some embodiments, from about 0.5to about 3. In addition, the fibers generally have an average diameterof from about 0.1 to about 20 micrometers, in some embodiments fromabout 0.5 to about 15 micrometers, and in some embodiments, from about 1to about 10 micrometers.

Once formed, the nonwoven web may then be bonded using any conventionaltechnique, such as with an adhesive or autogenously (e.g., fusion and/orself-adhesion of the fibers without an applied external adhesive).Autogenous bonding, for instance, may be achieved through contact of thefibers while they are semi-molten or tacky, or simply by blending atackifying resin and/or solvent with the aliphatic polyester(s) used toform the fibers. Suitable autogenous bonding techniques may includeultrasonic bonding, thermal bonding, through-air bonding, and so forth.

For instance, the web may be passed through a nip formed between a pairof rolls, one or both of which are heated to melt-fuse the fibers. Oneor both of the rolls may also contain intermittently raised bond pointsto provide an intermittent bonding pattern. The pattern of the raisedpoints is generally selected so that the nonwoven web has a total bondarea of less than about 50% (as determined by conventional opticalmicroscopic methods), and in some embodiments, less than about 30%.Likewise, the bond density is also typically greater than about 100bonds per square inch, and in some embodiments, from about 250 to about500 pin bonds per square inch. Such a combination of total bond area andbond density may be achieved by bonding the web with a pin bond patternhaving more than about 100 pin bonds per square inch that provides atotal bond surface area less than about 30% when fully contacting asmooth anvil roll. In some embodiments, the bond pattern may have a pinbond density from about 250 to about 350 pin bonds per square inch and atotal bond surface area from about 10% to about 25% when contacting asmooth anvil roll. Exemplary bond patterns include, for instance, thosedescribed in U.S. Pat. No. 3,855,046 to Hansen et al., U.S. Pat. No.5,620,779 to Levy et al., U.S. Pat. No. 5,962,112 to Haynes et al., U.S.Pat. No. 6,093,665 to Sayovitz et al., U.S. Design Pat. No. 428,267 toRomano et al. and U.S. Design Pat. No. 390,708 to Brown, which areincorporated herein in their entirety by reference thereto for allpurposes.

Due to the particular rheological and thermal properties of the modifiedaliphatic polyester used to form the fibers, the web bonding conditions(e.g., temperature and nip pressure) may be selected to cause thepolymer to melt and flow at relatively low temperatures. For example,the bonding temperature (e.g., the temperature of the rollers) may befrom about 50° C. to about 160° C., in some embodiments from about 80°C. to about 160° C., and in some embodiments, from about 100° C. toabout 140° C. Likewise, the nip pressure may range from about 5 to about150 pounds per square inch, in some embodiments, from about 10 to about100 pounds per square inch, and in some embodiments, from about 30 toabout 60 pounds per square inch.

In addition to meltblown webs, a variety of other nonwoven webs may alsobe formed from the modified aliphatic polyester in accordance with thepresent invention, such as spunbond webs, bonded carded webs, wet-laidwebs, airlaid webs, coform webs, hydraulically entangled webs, etc. Forexample, the polymer may be extruded through a spinnerette, quenched anddrawn into substantially continuous filaments, and randomly depositedonto a forming surface. Alternatively, the polymer may be formed into acarded web by placing bales of fibers formed from the blend into apicker that separates the fibers. Next, the fibers are sent through acombing or carding unit that further breaks apart and aligns the fibersin the machine direction so as to form a machine direction-orientedfibrous nonwoven web. Once formed, the nonwoven web is typicallystabilized by one or more known bonding techniques.

The fibers of the present invention may constitute the entire fibrouscomponent of the nonwoven web or blended with other types of fibers(e.g., staple fibers, filaments, etc). When blended with other types offibers, it is normally desired that the fibers of the present inventionconstitute from about 20 wt % to about 95 wt. %, in some embodimentsfrom about 30 wt. % to about 90 wt. %, and in some embodiments, fromabout 40 wt. % to about 80 wt. % of the total amount of fibers employedin the nonwoven web. For example, additional monocomponent and/ormulticomponent synthetic fibers may be utilized in the nonwoven web.Some suitable polymers that may be used to form the synthetic fibersinclude, but are not limited to: polyolefins, e.g., polyethylene,polypropylene, polybutylene, and so forth; polytetrafluoroethylene;polyesters, e.g., polyethylene terephthalate and so forth; polyvinylacetate; polyvinyl chloride acetate; polyvinyl butyral; acrylic resins,e.g., polyacrylate, polymethylacrylate, polymethylmethacrylate, and soforth; polyamides, e.g., nylon; polyvinyl chloride; polyvinylidenechloride; polystyrene; polyvinyl alcohol; polyurethanes; polylacticacid; etc. If desired, biodegradable polymers, such as poly(glycolicacid) (PGA), poly(lactic acid) (PLA), poly(β-malic acid) (PMLA),poly(ε-caprolactone) (PCL), poly(ρ-dioxanone) (PDS), poly(butylenesuccinate) (PBS), and poly(3-hydroxybutyrate) (PHB), may also beemployed. Some examples of known synthetic fibers include sheath-corebicomponent fibers available from KoSa Inc. of Charlotte, N.C. under thedesignations T-255 and T-256, both of which use a polyolefin sheath, orT-254, which has a low melt co-polyester sheath. Still other knownbicomponent fibers that may be used include those available from theChisso Corporation of Moriyama, Japan or Fibervisions LLC of Wilmington,Del. Synthetic or natural cellulosic polymers may also be used,including but not limited to, cellulosic esters; cellulosic ethers;cellulosic nitrates; cellulosic acetates; cellulosic acetate butyrates;ethyl cellulose; regenerated celluloses, such as viscose, rayon, and soforth.

The fibers of the present invention may also be blended with pulpfibers, such as high-average fiber length pulp, low-average fiber lengthpulp, or mixtures thereof. One example of suitable high-average lengthfluff pulp fibers includes softwood kraft pulp fibers. Softwood kraftpulp fibers are derived from coniferous trees and include pulp fiberssuch as, but not limited to, northern, western, and southern softwoodspecies, including redwood, red cedar, hemlock, Douglas fir, true firs,pine (e.g., southern pines), spruce (e.g., black spruce), combinationsthereof, and so forth. Northern softwood kraft pulp fibers may be usedin the present invention. An example of commercially available southernsoftwood kraft pulp fibers suitable for use in the present inventioninclude those available from Weyerhaeuser Company with offices inFederal Way, Wash. under the trade designation of “NB-416.” Anothersuitable pulp for use in the present invention is a bleached, sulfatewood pulp containing primarily softwood fibers that is available fromBowater Corp. with offices in Greenville, S.C. under the trade nameCoosAbsorb S pulp. Low-average length fibers may also be used in thepresent invention. An example of suitable low-average length pulp fibersis hardwood kraft pulp fibers. Hardwood kraft pulp fibers are derivedfrom deciduous trees and include pulp fibers such as, but not limitedto, eucalyptus, maple, birch, aspen, etc. Eucalyptus kraft pulp fibersmay be particularly desired to increase softness, enhance brightness,increase opacity, and change the pore structure of the sheet to increaseits wicking ability.

Nonwoven laminates may also be formed in which one or more layers areformed from the modified aliphatic polyester of the present invention.In one embodiment, for example, the nonwoven laminate contains ameltblown layer positioned between two spunbond layers to form aspunbond/meltblown/spunbond (“SMS”) laminate. If desired, the meltblownlayer may be formed from the modified aliphatic polyester. The spunbondlayer may be formed from the modified aliphatic polyester, otherbiodegradable polymer(s), and/or any other polymer (e.g., polyolefins).Various techniques for forming SMS laminates are described in U.S. Pat.No. 4,041,203 to Brock et al.; U.S. Pat. No. 5,213,881 to Timmons, etal.; U.S. Pat. No. 5,464,688 to Timmons, et al.; U.S. Pat. No. 4,374,888to Bornslaeger; U.S. Pat. No. 5,169,706 to Collier, et al.; and U.S.Pat. No. 4,766,029 to Brock et al., as well as U.S. Patent ApplicationPublication No. 2004/0002273 to Fitting, et al., all of which areincorporated herein in their entirety by reference thereto for allpurposes. Of course, the nonwoven laminate may have other configurationand possess any desired number of meltblown and spunbond layers, such asspunbond/meltblown/meltblown/spunbond laminates (“SMMS”),spunbond/meltblown laminates (“SM”), etc. Although the basis weight ofthe nonwoven laminate may be tailored to the desired application, itgenerally ranges from about 10 to about 300 grams per square meter(“gsm”), in some embodiments from about 25 to about 200 gsm, and in someembodiments, from about 40 to about 150 gsm.

If desired, the nonwoven web or laminate may be applied with varioustreatments to impart desirable characteristics. For example, the web maybe treated with liquid-repellency additives, antistatic agents,surfactants, colorants, antifogging agents, fluorochemical blood oralcohol repellents, lubricants, and/or antimicrobial agents. Inaddition, the web may be subjected to an electret treatment that impartsan electrostatic charge to improve filtration efficiency. The charge mayinclude layers of positive or negative charges trapped at or near thesurface of the polymer, or charge clouds stored in the bulk of thepolymer. The charge may also include polarization charges that arefrozen in alignment of the dipoles of the molecules. Techniques forsubjecting a fabric to an electret treatment are well known by thoseskilled in the art. Examples of such techniques include, but are notlimited to, thermal, liquid-contact, electron beam and corona dischargetechniques. In one particular embodiment, the electret treatment is acorona discharge technique, which involves subjecting the laminate to apair of electrical fields that have opposite polarities. Other methodsfor forming an electret material are described in U.S. Pat. No.4,215,682 to Kubik, et al.; U.S. Pat. No. 4,375,718 to Wadsworth; U.S.Pat. No. 4,592,815 to Nakao; U.S. Pat. No. 4,874,659 to Ando; U.S. Pat.No. 5,401,446 to Tsai, et al.; U.S. Pat. No. 5,883,026 to Reader, etal.; U.S. Pat. No. 5,908,598 to Rousseau, et al.; U.S. Pat. No.6,365,088 to Knight, et al., which are incorporated herein in theirentirety by reference thereto for all purposes.

The nonwoven web or laminate may be used in a wide variety ofapplications. For example, the web may be incorporated into a “medicalproduct”, such as gowns, surgical drapes, facemasks, head coverings,surgical caps, shoe coverings, sterilization wraps, warming blankets,heating pads, and so forth. Of course, the nonwoven web may also be usedin various other articles. For example, the nonwoven web may beincorporated into an “absorbent article” that is capable of absorbingwater or other fluids. Examples of some absorbent articles include, butare not limited to, personal care absorbent articles, such as diapers,training pants, absorbent underpants, incontinence articles, femininehygiene products (e.g., sanitary napkins), swim wear, baby wipes, mittwipe, and so forth; medical absorbent articles, such as garments,fenestration materials, underpads, bedpads, bandages, absorbent drapes,and medical wipes; food service wipers; clothing articles; pouches, andso forth. Materials and processes suitable for forming such articles arewell known to those skilled in the art. Absorbent articles, forinstance, typically include a substantially liquid-impermeable layer(e.g., outer cover), a liquid-permeable layer (e.g., bodyside liner,surge layer, etc.), and an absorbent core. In one embodiment, forexample, the nonwoven web of the present invention may be used to forman outer cover of an absorbent article.

The present invention may be better understood with reference to thefollowing examples.

Test Methods

Molecular Weight:

The molecular weight distribution of a polymer was determined by gelpermeation chromatography (“GPC”). The samples were initially preparedby adding 0.5% wt/v solutions of the sample polymers in chloroform to40-milliliter glass vials. For example, 0.05±0.0005 grams of the polymerwas added to 10 milliliters of chloroform. The prepared samples wereplaced on an orbital shaker and agitated overnight. The dissolved samplewas filtered through a 0.45-micrometer PTFE membrane and analyzed usingthe following conditions:

-   Columns: Styragel HR 1, 2, 3, 4, & 5E (5 in series) at 41° C.-   Solvent/Eluent: Chloroform @ 1.0 milliliter per minute-   HPLC: Waters 600E gradient pump and controller, Waters 717 auto    sampler-   Detector: Waters 2414 Differential Refractometer at sensitivity=30,    at 40° C. and scale factor of 20-   Sample Concentration: 0.5% of polymer “as is”-   Injection Volume: 50 microliters-   Calibration Standards Narrow MW polystyrene, 30-microliter injected    volume.

Number Average Molecular Weight (MW_(n)), Weight Average MolecularWeight (MW_(w)) and first moment of viscosity average molecular weight(MW_(z)) were obtained.

Apparent Viscosity:

The rheological properties of polymer samples were determined using aGöttfert Rheograph 2003 capillary rheometer with WinRHEO version 2.31analysis software. The setup included a 2000-bar pressure transducer anda 30/1:0/180 roundhole capillary die. Sample loading was done byalternating between sample addition and packing with a ramrod. A2-minute melt time preceded each test to allow the polymer to completelymelt at the test temperature (usually 150° C. to 220° C.). The capillaryrheometer determined the apparent viscosity (Pa·s) at various shearrates, such as 100, 200, 500, 1000, 2000, and 4000 s⁻¹. The resultantrheology curve of apparent shear rate versus apparent viscosity gave anindication of how the polymer would run at that temperature in anextrusion process.

Melt Flow Index:

The melt flow index is the weight of a polymer (in grams) forced throughan extrusion rheometer orifice (0.0825-inch diameter) when subjected toa load of 2160 grams in 10 minutes (usually 150° C. to 230° C.). Unlessotherwise indicated, the melt flow index was measured in accordance withASTM Test Method D1238-E.

Thermal Properties:

The melting temperature (“T_(m)”), glass transition temperature(“T_(g)”), and latent heat of fusion (“ΔH_(f)”) were determined bydifferential scanning calorimetry (DSC). The differential scanningcalorimeter was a THERMAL ANALYST 2910 Differential ScanningCalorimeter, which was outfitted with a liquid nitrogen coolingaccessory and with a THERMAL ANALYST 2200 (version 8.10) analysissoftware program, both of which are available from T.A. Instruments Inc.of New Castle, Del. To avoid directly handling the samples, tweezers orother tools were used. The samples were placed into an aluminum pan andweighed to an accuracy of 0.01 milligram on an analytical balance. A lidwas crimped over the material sample onto the pan. Typically, the resinpellets were placed directly in the weighing pan, and the fibers werecut to accommodate placement on the weighing pan and covering by thelid.

The differential scanning calorimeter was calibrated using an indiummetal standard and a baseline correction was performed, as described inthe operating manual for the differential scanning calorimeter. Amaterial sample was placed into the test chamber of the differentialscanning calorimeter for testing, and an empty pan is used as areference. All testing was run with a 55-cubic centimeter per minutenitrogen (industrial grade) purge on the test chamber. For resin pelletsamples, the heating and cooling program was a 2-cycle test that beganwith an equilibration of the chamber to −50° C., followed by a firstheating period at a heating rate of 10° C. per minute to a temperatureof 200° C., followed by equilibration of the sample at 200° C. for 3minutes, followed by a first cooling period at a cooling rate of 20° C.per minute to a temperature of −50° C., followed by equilibration of thesample at −50° C. for 3 minutes, and then a second heating period at aheating rate of 10° C. per minute to a temperature of 200° C. For fibersamples, the heating and cooling program was a 1-cycle test that beganwith an equilibration of the chamber to −50° C., followed by a heatingperiod at a heating rate of 20° C. per minute to a temperature of 200°C., followed by equilibration of the sample at 200° C. for 3 minutes,and then a cooling period at a cooling rate of 10° C. per minute to atemperature of −50° C. All testing was run with a 55-cubic centimeterper minute nitrogen (industrial grade) purge on the test chamber.

The results were then evaluated using the THERMAL ANALYST 2200 analysissoftware program, which identified and quantified the glass transitiontemperature of inflection, the endothermic and exothermic peaks, and theareas under the peaks on the DSC plots. The glass transition temperaturewas identified as the region on the plot-line where a distinct change inslope occurred, and the melting temperature was determined using anautomatic inflection calculation. The areas under the peaks on the DSCplots were determined in terms of joules per gram of sample (J/g). Forexample, the endothermic heat of melting of a resin or fiber sample wasdetermined by integrating the area of the endothermic peak. The areavalues were determined by converting the areas under the DSC plots (e.g.the area of the endotherm) into the units of joules per gram (J/g) usingcomputer software.

Tensile Properties:

The strip tensile strength values were determined in substantialaccordance with ASTM Standard D-5034. Specifically, a nonwoven websample was cut or otherwise provided with size dimensions that measured25 millimeters (width)×127 millimeters (length). Aconstant-rate-of-extension type of tensile tester was employed. Thetensile testing system was a Sintech Tensile Tester, which is availablefrom Sintech Corp. of Cary, N.C. The tensile tester was equipped withTESTWORKS 4.08B software from MTS Corporation to support the testing. Anappropriate load cell was selected so that the tested value fell withinthe range of 10-90% of the full scale load. The sample was held betweengrips having a front and back face measuring 25.4 millimeters×76millimeters. The grip faces were rubberized, and the longer dimension ofthe grip was perpendicular to the direction of pull. The grip pressurewas pneumatically maintained at a pressure of 40 pounds per square inch.The tensile test was run at a 300-millimeter per minute rate with agauge length of 10.16 centimeters and a break sensitivity of 40%.

Five samples were tested by applying the test load along themachine-direction and five samples were tested by applying the test loadalong the cross direction. In addition to tensile strength, the peakload, peak elongation (i.e., % strain at peak load), and the energy topeak were measured. The peak strip tensile loads from each specimentested were arithmetically averaged to determine the MD or CD tensilestrength.

EXAMPLE 1

A polybutylene succinate resin was initially obtained from IRE Chemicalsunder the designation ENPOL™ 4500J. The resin was then melt blended witha reactant solution. The reactant solution contained varying percentagesof an alcohol (“reactant”) and dibutyltin diacetate (DBDA) as acatalyst. Each sample employed 1,4-butanediol as the alcohol except forSample 2, which employed ethylene glycol diacetate (EGDA). The solutionwas fed by an Eldex pump to the Feed/Vent port of a co-rotating,twin-screw extruder (USALAB Prism H16, diameter: 16 mm, L/D of 40/1)manufactured by Thermo Electron Corporation. The screw length was 25inches. The extruder had one die opening having a diameter of 3millimeters. Upon formation, the extruded resin was cooled on afan-cooled conveyor belt and formed into pellets by a Conair pelletizer.Reactive extrusion parameters were monitored on the USALAB Prism H16extruder during the reactive extrusion process. The conditions are shownbelow in Table 1. The resulting Samples 1 and 3-11 were hydroxybutylterminated PBS.

TABLE 1 Reactive Extrusion Process Conditions for modifying PBS on aUSALAB Prism H16 Sample Temperature (° C.) Screw Speed Resin RateReactant Catalyst No. Zone 1, 2, 3-8, 9, 10 (rpm) (lb/h) (% of resinrate) (% of resin rate) Control 1 90 125 165 125 110 150 1.9 0 0 1 90125 165 125 110 150 1.9 4 0 2 90 125 165 125 110 150 1.9 4(EGDA) 0.08 390 125 165 125 110 150 2 3.3 0.08 4 90 125 165 125 110 150 2 1.7 0.04 590 125 165 125 110 150 2 5.2 0.12 6 90 125 165 125 110 150 2 1.7 0.02 790 125 165 125 110 150 2 3.3 0.04 8 90 125 165 125 110 150 2 5.2 0.06 990 125 165 125 110 150 2 1.7 0.08 10 90 125 165 125 110 150 2 3.3 0.1611 90 125 165 125 110 150 2 5.2 0.24

The melt rheology was studied for the unmodified sample and modifiedsamples (Samples 1-11). The measurement was carried out on a GöettfertRheograph 2003 (available from Göettfert of Rock Hill, S.C.) at 150° C.with a 30/1 (Length/Diameter) mm/mm die. The apparent melt viscosity wasdetermined at apparent shear rates of 100, 200, 500, 1000, 2000 and 4000s⁻¹. The apparent melt viscosities at the various apparent shear rateswere plotted and the rheology curves were generated as shown in FIG. 2.As illustrated, the apparent viscosity of the Enpol™ 4500J controlsample (unmodified resin) was higher than the apparent viscosities ofSamples 1, 3-11. The viscosity of Sample 2, however, was similar to thecontrol, suggesting that transesterification between PBS and EGDA wasnot significant. The melt flow indices of several of the samples werealso determined with a Tinius Olsen Extrusion plastometer (170° C., 2.16kg). Further, the samples were subjected to molecular weight (MW)analysis by GPC with narrow MW distribution polystyrenes as standards.The results are set forth below in Table 2.

TABLE 2 Properties of modified PBS on a USALAB Prism H16 Apparentviscosity (Pa · s) at Melt Flow rate Sample apparent shear (g/10 min at170° C. Mw Mn Polydispersity No. rate of 1000 l/s and 2.16 kg) (g/mol)(Mw/Mn) Control 1 155 8 128000 73900 1.73 1 68 86 96900 58200 1.66 2 154N/A N/A N/A N/A 3 28.5 290 77200 42000 1.84 4 85 56 101900 64700 1.58 59.8 852 65800 35200 1.87 6 163 50 97500 57500 1.69 7 37 185 86400 536001.61 8 11.4 840 61100 32400 1.87 9 65 83 99900 59500 1.68 10 14 60067200 37000 1.82 11 4.9 1100 58600 31600 1.85

As indicated, the melt flow indices of the modified resins (Samples 1,3-11) were significantly greater than the control sample. In addition,the weight average molecular weight (M_(w)) and number average molecularweight (M_(n)) were decreased in a controlled fashion, which confirmedthat the increase in melt flow index was due to alcoholysis.

EXAMPLE 2

An aliphatic polyester resin (polybutylene succinate, PBS) was initiallyobtained from IRE Chemicals under the designation ENPOL™ 4500J. Aco-rotating, twin-screw extruder was employed (ZSK-30, diameter) thatwas manufactured by Werner and Pfleiderer Corporation of Ramsey, N.J.The screw length was 1328 millimeters. The extruder had 14 barrels,numbered consecutively 1-14 from the feed hopper to the die. The firstbarrel (#1) received the ENPOL™ 4500J resin via a volumetric feeder at athroughput of 40 pounds per hour. The fifth barrel (#5) received areactant solution via a pressurized injector connected with an Eldexpump. The reactant solution contained 1,4-butanediol (87.5 wt. %),ethanol (6.25 wt. %), and titanium propoxide (6.25 wt. %). The screwspeed was 150 revolutions per minute (“rpm”). The die used to extrudethe resin had 4 die openings (6 millimeters in diameter) that wereseparated by 4 millimeters. Upon formation, the extruded resin wascooled on a fan-cooled conveyor belt and formed into pellets by a Conairpelletizer. Reactive extrusion parameters were monitored during thereactive extrusion process. The conditions are shown below in Table 3.

TABLE 3 Process conditions for reactive extrusion of PBS with1,4-Butanediol on a ZSK-30 extruder Reactants Resin Titanium ExtruderSamples feeding Butanediol Propoxide speed Extruder temperature profile(° C.) Torque No. rate (lb/h) (%) (ppm) (rpm) T₁ T₂ T₃ T₄ T₅ T₆ T₇T_(melt) P_(melt) (%) Control 2 40 0 0 150 160 180 180 180 180 170 110122 130-140 57-60 12 40 0.5 0 150 162 178 183 184 182 176 102 115110-120 52-55 13 40 0.5 312 150 163 178 181 179 184 173 102 115 80 48-5014 40 0.7 438 150 154 176 180 174 176 166 106 118 50 46-48

As indicated, the addition of 0.5 wt. % butanediol alone (Sample 12) didnot significantly decrease the torque of the control sample, althoughthe die pressure did drop somewhat. With the addition of 0.7 wt. %1,4-butanediol and 438 ppm titanium propoxide (Sample 14), the diepressure decreased to a greater extent. The torque and die pressurecould be proportionally adjusted with the change of reactant andcatalyst.

Melt rheology tests were also performed with the “Control 2” sample andSamples 12-14 on a Göettfert Rheograph 2003 (available from Göettfert inRock Hill, S.C.) at 150° C. with 30/1 (Length/Diameter) mm/mm die. Theapparent melt viscosity was determined at apparent shear rates of 100,200, 500, 1000, 2000 and 4000 s⁻¹. The results are shown in FIG. 3. Asindicated, Samples 12-14 had lower apparent viscosities over the entirerange of shear rates than the “Control 2” sample. The melt flow index ofthe sample was determined by the method of ASTM D1239, with a TiniusOlsen Extrusion Plastometer at 150° C. and 2.16 kg. Further, the sampleswere subjected to molecular weight (MW) analysis by GPC with narrow MWpolystyrenes as standards. The results are set forth below in Table 4.Hydroxybutyl terminated PBS samples were produced in Sample 12-14.

TABLE 4 Properties of modified PBS on the ZSK-30 Melt Apparent IndexViscosity (g/10 M_(w) M_(n) Polydispersity Tm Enthalpy Sample (Pa · s)min) (g/mol) (M_(w)/M_(n)) (° C.) (J/g) Control 2 150 25.8 112300 692001.62 112.5 56.6 12 112 39.3 104900 65800 1.6 112.6 53.7 13 100 52.999700 61900 1.61 112.7 53.2 14 75 80.4 93300 55700 1.67 112.7 53.9

As indicated, the melt flow indices of the modified resins (Samples12-14) were significantly greater than the control sample.

EXAMPLE 3

A modified PBS resin of Example 2 (Sample 14) was used to form ameltblown web (“MB”). Meltblown spinning was conducted with a pilot linethat included a Killion extruder with a single screw diameter of 1.75inches (Verona, N.Y.); a 10-feet hose from Dekoron/Unitherm (RivieraBeach, Fla.); and a 14-inch meltblown die with an 11.5-inch spray and anorifice size of 0.015 inch. The modified resin was fed via gravity intothe extruder and then transferred into the hose connected with themeltblown die. A control sample was also tested that was formed from 20pounds of a polypropylene resin obtained from ExxonMobil under thedesignation “PF-015.” Table 5 shows the process conditions used duringspinning.

TABLE 5 Processing conditions of modified PBS MB spinning Extruder ScrewPrimary Air Sample Zone 1 Zone 2 Zone 3 Zone 4 Speed Torque PressureHose Die Temperature Pressure No. (F) (F) (F) (F) (rpm) (Amps) (Psi) (F)(F) (F) (Psi) PF-015 350 380 380 400 20 2 50 400 415 460 40 14 300 318334 338 22 2 77 350 358 385 45

The tensile properties of modified polyester meltblown nonwoven samplesof different basis weight were tested. The results are listed in Table6. SD is standard deviation. “Peak Load” is given in units ofpounds-force (lbf), and “Energy to Peak” is given in units ofpound-force*inch (lbf*in).

TABLE 6 PBS MB Samples measured with 1″ × 6″ strips Peak Load (lbf)Strain at Peak (%) Energy to Peak (lbf*in) Sample Basis Weight (gsm)Mean SD Mean SD Mean SD Machine Direction 16 gsm PP 16.5 0.73 0.12 16.47.1 0.4 0.2 23 gsm PP 21.2 1.07 0.16 21.3 8 0.81 0.41 23 gsm PBS 23.21.56 0.19 35.7 14.4 1.8 0.9 17 gsm PBS 17.5 1.14 0.07 34.7 12.2 1.220.58  9 gsm PBS 9.3 0.48 0.05 30.8 4 0.41 0.08 Cross Direction 16 gsm PP18.6 0.56 0.03 29 5.7 0.54 0.14 23 gsm PP 22.2 0.72 0.06 24.9 13.8 0.610.42 23 gsm PBS 22.7 0.81 0.09 37.9 16.4 0.94 0.53 17 gsm PBS 17 0.610.03 38.9 6.8 0.69 0.16  9 gsm PBS 8.8 0.26 0.04 37.2 12.9 0.27 0.16

As indicated, the samples formed from the modified aliphatic polyesterhad a higher peak load and % strain at peak than polypropylene webs ofthe same basis weight. A sample of the modified aliphatic polyester webwas also collected and analyzed with an electronic scanning microscope(“SEM”) at different magnitudes. A micron scale bar was imprinted oneach photo to permit measurements and comparisons. FIGS. 4 and 5 showthe images of 17 gsm PBS meltblown fiber web at 500× and 1000×,respectively.

While the invention has been described in detail with respect to thespecific embodiments thereof, it will be appreciated that those skilledin the art, upon attaining an understanding of the foregoing, mayreadily conceive of alterations to, variations of, and equivalents tothese embodiments. Accordingly, the scope of the present inventionshould be assessed as that of the appended claims and any equivalentsthereto.

What is claimed is:
 1. A method for forming a biodegredable polymer foruse in fiber formation, the method comprising melt blending a firstaliphatic polyester with at least one alcohol so that the polyesterundergoes an alcoholysis reaction, wherein the alcohol is employed in anamount of from about 0.1 wt.% to about 20 wt.%, based on the weight ofthe first aliphatic polyester, and wherein a catalyst is employed tofacilitate the alcoholysis reaction, the alcoholysis reaction resultingin a second, modified aliphatic polyester having a melt flow index thatis greater than the melt flow index of the first polyester, determinedat a load of 2160 grams and temperature of 170° C. in accordance withASTM Test Method D1238-E.
 2. The method of claim 1, wherein the ratio ofthe melt flow index of the second aliphatic polyester to the melt flowindex of the first aliphatic polyester is at least about 1.5.
 3. Themethod of claim 1, wherein the ratio of the melt flow index of thesecond aliphatic polyester to the melt flow index of the first aliphaticpolyester is at least about
 50. 4. The method of claim 1, wherein theratio of the apparent viscosity of the first aliphatic polyester to theapparent viscosity of the second aliphatic polyester is at least about1.1, determined at a temperature of 150° C. and a shear rate of 1000sec⁻¹.
 5. The method of claim 1, wherein the ratio of the apparentviscosity of the first aliphatic polyester to the apparent viscosity ofthe second aliphatic polyester is at least about 2, determined at atemperature of 150° C. and a shear rate of 1000 sec⁻¹.
 6. The method ofclaim 1, wherein the second aliphatic polyester has a number averagemolecular weight of from about 10,000 to about 70,000 grams per mole anda weight average molecular weight of from about 20,000 to about 125,000grams per mole.
 7. The method of claim 1, wherein the second aliphaticpolyester has a number average molecular weight of from about 20,000 toabout 60,000 grams per mole and a weight average molecular weight offrom about 40,000 to about 80,000 grams per mole.
 8. The method of claim1, wherein the polydispersity index of the first and second aliphaticpolyesters is from about 1.1 to about 2.0.
 9. The method of claim 1,wherein the first and second aliphatic polyesters both have a meltingpoint of from about 80° C. to about 160° C.
 10. The method of claim 1,wherein the first and second aliphatic polyesters both have a glasstransition temperature of about 0° C. or less,
 11. The method of claim1, wherein the melt flow index of the second aliphatic polyester is fromabout 5 to about 1000 grams per 10 minutes.
 12. The method of claim 1,wherein the melt flow index of the second aliphatic polyester is fromabout 100 to about 700 grams per 10 minutes.
 13. The method of claim 1,wherein the second aliphatic polyester has an apparent viscosity of fromabout 5 to about 500 Pascal-seconds, determined at a temperature of 150°C. and a shear rate of 1000 sec⁻¹.
 14. The method of claim 1, whereinthe second aliphatic polyester has an apparent viscosity of from about15 to about 100 Pascal-seconds, determined at a temperature of 150° C.and a shear rate of 1000 sec⁻¹.
 15. The method of claim 1, wherein thesecond aliphatic polyester is terminated with an alkyl group,hydroxyalkyl group, or a combination thereof.
 16. The method of claim15, wherein the second aliphatic polyester has the following generalstructure:

wherein, m is an integer from 2 to 10; n is an integer from 0 to 18; yis an integer greater than 1; and R₁ and R₂ are independently selectedfrom hydrogen; hydroxyl groups; straight chain or branched, substitutedor unsubstituted C₁-C₁₀ alkyl groups; and straight chain or branched,substituted or unsubstituted C₁-C₁₀ hydroxalkyl groups.
 17. The methodof claim 16, wherein m and n are each from 2 to
 4. 18. The method ofclaim 1, wherein the second aliphatic polyester is a succinate-basedpolymer.
 19. The method of claim 18, wherein the succinate-based polymeris polybutylene succinate or a copolymer thereof.
 20. The method ofclaim 1, wherein the alcohol is employed in an amount of from about 0.5wt.% to about 5 wt.%, based on the weight of the first aliphaticpolyester.
 21. The method of claim 1, wherein the alcohol is amonohydric alcohol.
 22. The method of claim 1, wherein the alcohol is apolyhydric alcohol.
 23. The method of claim 22, wherein the alcohol is adihydric alcohol.
 24. The method of claim 1, wherein the catalyst is atransition metal catalyst based on a Group IVA metal, a Group IVB metal,or a combination thereof.
 25. The method of claim 1, wherein thecatalyst is employed in an amount of from about 50 to about 2000 partsper million of the first polyester.
 26. The method of claim 1, whereinthe alcoholysis reaction is conducted in the presence of a co-solvent.27. The method of claim 1, wherein melt blending occurs at a temperatureof from about 50° C. to about 300° C. and an apparent shear rate of fromabout 100 seconds⁻¹ to about 10,000 seconds⁻¹.
 28. The method of claim1, wherein melt blending occurs at a temperature of from about 90° C. toabout 180° C. and an apparent shear rate of from about 800 seconds⁻¹ toabout 1200 seconds⁻¹.
 29. The method of claim 1, wherein melt blendingoccurs within an extruder.
 30. The method of claim 1, wherein the secondaliphatic polyester is extruded through a meltblowing die.